Colombia delayed peace talks with Marxist ELN rebels until they free a politician held captive for six months, President Juan Manuel Santos said on Thursday, as he struggles to refloat another peace deal with FARC guerrillas after it was rejected in a plebiscite.

The National Liberation Army (ELN), the nation's second-biggest insurgent group, must release Odin Sanchez to the International Committee of the Red Cross before talks can begin in Ecuador, Santos said, reiterating a condition he set months ago.

The opening ceremony had been scheduled to take place in Ecuador's capital, but it was canceled at the last minute. The government said the talks could still go forward as early as Friday or Saturday if the rebels free Sanchez, however.

The 2,000-strong ELN, considered a terrorist group by the United States and European Union, has kidnapped hundreds of people during its 52-year insurgency to raise war funds and use hostages as bargaining chips with the government.

Peace Prize winner

Santos won the 2016 Nobel Peace Prize earlier this month for his efforts to end a conflict with the leftist Revolutionary Armed Forces of Colombia (FARC), a surprising choice given voters narrowly shunned the deal he signed with them.

More than 220,000 people have been killed in Colombia's long-running armed conflict, which has pitted leftist guerrillas against right-wing paramilitary groups and the security forces.

Founded by radical Catholic priests and inspired by Cuba's 1959 revolution, the ELN has been in on-and-off closed-door talks with the government since 2014 on how the two sides would conduct negotiations.

The rebels have remained active during that time, kidnapping and bombing oil installations, though in recent months they have released some captives.

Formal peace talks would likely mirror those held with the FARC. The peace agreement, signed on Sept. 26 with the FARC, was internationally lauded but criticized by many in Colombia for being too lenient on the rebels.

'No' side wins referendum

Former President Alvaro Uribe is now leading the effort to change the agreement that would have given the FARC guaranteed congressional seats and immunity from traditional jail sentences. The "no" side won the plebiscite by less than half a percentage point.

Peace with the two groups is unlikely to put a complete end to violence in a country also ravaged by unrest from drug trafficking and other crimes, but it would allow economic development in once off-limits areas and shift more military resources to fight growing criminal gangs.